在实体框架中定义集合而不创建关系

Question

I have two classes Song and Album . Album has nested collection of songs. But in EF I have to create relationships between. But Song can be single or without Album . So I want create something like that in database.

public class Song:IEntity
{
    public Song()
    {
        Id = Guid.NewGuid().ToString();
    }
    public string Id { get; set; }
    public string Artist { get; set; }
    public string Title { get; set; }

}

public class Album:IEntity
{
    public Album()
    {
        Id = Guid.NewGuid().ToString();
    }
    public string Id { get; set; }
    public string Artist { get; set; }
    public string Title { get; set; }
    public DateTime Year { get; set; }
    public virtual ICollection<Song> Songs { get; set; }
}

Answer 1

Ok, and what is not working? Your model looks fine besides depriving yourself from ability to check if Song is part of any album or not.

Many-Many nad 1-Many relationships are translated into seperate tables, until you add relationship between certain instances you don't lose any memory. Is there any reason why not to add: public Album Album {get;set;} to the Album , there is something like null you know?

Answer 2

Update your Song class to:

public class Song:IEntity
{
    public Song()
    {
        Id = Guid.NewGuid().ToString();
    }
    public virtual Album Album { get; set; }. //add this line
    public string Id { get; set; }
    public string Artist { get; set; }
    public string Title { get; set; }
}

And define following mapping in your DbContext :

protected override void OnModelCreating(DbModelBuilder modelBuilder) 
{ 
     modelBuilder.Entity<Song>() 
            .HasOptional(c => c.Album) 
            .WithMany(t => t.Songs);
}